Blending hydrogenated fractions to make a jet fuel



United States Patent 3,493,491 BLENDING HYDROGENATED FRACTIONS TO MAKE AJET FUEL Robert L. Barnes, Placentia, and Robert Dinsmore,

Long Beach, Calif., assignors to Atlantic Rlchfield Colt!- pany,Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Originalapplication Aug. 3, 1967, Ser. No. 658,066. Divided and this applicationMay 21, 1969,

Ser. No. 839,128

Int. Cl. C101 1/04; C07c /02 US. Cl. 208144 10 Claims ABSTRACT OF THEDISCLOSURE A high thermal stability, low vapor pressure jet engine fuelfor Mach 3 to 3.5 aircraft containing from 30 to 60 percentisoparaffins, from to 50 percent monocyclic naphthenes, and from 10 topercent polycyclic naphthenes. The fuel is formed by removingn-paraffins from a highly parafiinic crude and/ or by blendingisoparaffinic stocks together with straight run stocks to form thedesired proportion of constituents. Preferred blending materials arealkylation unit solvent rerun bottoms, alkyl trimers, propylenetetramers, specific thermally cracked stocks boiling within the stoveoil range, and specific straight run stocks boiling in the stove oilrange. The thermally cracked stocks and straight run stocks used arefirst hydrogenated to completion in two hydrogenation steps, treated toremove n-paraffins and then blended toform the specific fuelcomposition. The alkylation unit solvent rerun bottoms and propylenetetramer are substantially isoparaffinic and require only a singlehydrogenation step prior to blending.

CROSS REFERENCE TO RELATED APPLICATIONS This is a division of patentapplication Ser. No. 65 8,066, filed Aug. 3, 1967, now abandoned, forJet Fuel, which is a continuation-in-part of application Ser. No.588,237, filed Oct. 13, 1966, now Patent No. 3,367,860 which is acontinuation-in-part of application Ser. No. 324,881, filed Nov. 19,1963, now abandoned.

BACKGROUND OF THE INVENTION This invention is directed to a high thermalstability, low vapor pressure fuel for jet engines in Mach 3 to 3.5aircraft and to the process for producing such fuels and operating suchengines. These engines require fuel having a high luminometer number, ahigh heat of combustion, a low freeze point, a low viscosity at lowtemperatures and a moderately high flash point. In addition to theseburning properties, the fuel must be of high thermal stability attemperatures of about 700 F. The required burning properties and thermalstability have been found to be generally unattainable with straight runstocks.

The heat of combustion may be expressed both as B.t.u./ gal. andB.t.u./lb. For simplicity in nomenclature, the heat of combustionexpressed in B.t.u./gal. will be referred to herein as fuel density. Allpercentages of fuel components given herein are intended to refer topercent by volume unless specified otherwise.

Many of the fuels developed thus far for use in Mach 3 to 3.5 aircrafthave been unsatisfactory in that the luminometer number has beenundesirably low. The luminometer number is indicative of the tendency ofthe fuel to smoke during combustion in the engine. High luminometernumber fuels burn cleaner than those of lower luminometer number and,consequently, provide a more 3,493,491 Patented Feb. 3, 1970 desirablejet fuel. Preferably, the luminometer number of a Mach 3 to 3.5 jetaircraft fuel should be or greater.

The luminometer number of a jet fuel can be increased generally byincreasing its paraffinicity. Increased paraffinicity, however, alsonormally causes a rise in the fuel freeze point and a decrease in thefuel density due to the comparatively high hydrogen to carbon ratio ofthe paraffins. It has now been discovered that the removal of normalparaffins from the paraffin content of the fuel significantly reducesthe detrimental effect of the parafiins on fuel freeze point withoutotherwise reducing the beneficial effects of high parafiinicity. Thebranched or isoparaflins still beneficially increase the fuelluminometer number but the freeze point remains low and surprisinglyonly a mild reduction in fuel density has been observed. Also, contraryto some teachings of the prior art, it has been found that jet fuels ofthis invention having high isoparatfin content also have good stabilityat high temperatures.

The most desirable fuel, it has now been discovered comprises narrowcompositional ranges of isoparaflins, monocyclic naphthenes andpolycyclic naphthenes. A small amount of normal paratfins can also betolerated when the ratio of isoparafiins to normal paraffins is kepthigh.

SUMMARY OF INVENTION The low vapor pressure, high thermal stability jetfuel compositions of this invention contain from 30 to 60 percentisoparaffins, up to about 6.5 percent n-paraffins, from a 20 to 50percent monocyclic naphthenes and from 10 to 25 percent polycyclicnaphthenes. The fuels are hydrogenated to completion and containsubstantially no aromatics. These fuel compositions possess excellentburning characteristics and are thermally stable at temperatures on theorder of 700 F. They have a heat of combustion of greater than 18,750B.t.u./lb., a fuel density of greater than 124,000 B.t.u./gal., and aluminometer number of greater than 75. The fuel freeze points of thesefuels are about 75 F. or lower. These jet fuels are formed by blendingselect, completely hydrogenated stocks in the proper proportions toobtain the ranges of components and properties set forth.

In particular, blending components which have shown exceptionallybeneficial characteristics are hydrogenated alkylation unit rerunbottoms, hydrogenated propylene tetramers, thermally cracked stock whichhas been hydrogenated and treated to remove n-paraffins, andhydrogenated stove oils from high normal parafiin content crudes whichhave been treated with a molecular sieve or in some other manner toremove n-paraffins.

The alkylation unit rerun bottoms blending components of this inventionboil in the range of 370 to 525 F. and typically are a distribution of Cto C isoparafiins in the following ranges:

Percent by volume c 815 (3 30-40 0 10 25 c 10-25 0 8-15 c 8-15 3 122,500B.t.u./ gal. and a freze point below 80 F. The viscosity of the alkytrimers and their luminometer number are also excellent so that theyprovide a low boiling point high heat of combustion stock which can beused for blending to provide the desired properties of a high Mach jetfuel.

The propylene tetramer blending component of this invention is also arefinery product boiling in the range from 365 to 445 F. and comprisingolefins from 50 to 70 percent C up to about 27 percent C from 3 to 45percent C and up to 5 percent C The tetramer when hydrogenated has anAPI gravity of 53.5, a heat of combustion of 18,980 B.t.u./lb., a fueldensity of 120,860 B.t.u./gal., a freeze point below 80 F. and aluminometer number of 115 and is substantially 100 percent isoparaflin.The preferred tetramer blending component is the light tetramer whichcontains about 27 percent C olefins, about 70 percent C olefins, andabout 3 percent C olefins.

One object of this invention is to produce a fuel for jet engines ofMach 3 to 3.5 aircraft.

Another object of this invention is to provide a jet fuel which has aflash point of 150 F. minimum, a gravity (API) of 44 minimum, aviscosity at 30 F. of 15 maximum, a freeze point of -70 F. maximum, 21heat of combustion of at least 18,750 B.t.u./lb., a fuel density of atleast 124,000 B.t.u./gal., and a luminometer number of at least 80.

Another object of this invention is to produce a jet fuel which issubstantially free of normal paraffins and has an isoparaffin content offrom 30 to 60 percent by volume with the balance naphthenes.

These and other objects of this invention will become more apparent fromthe following discussion and the appended claims.

PREFERRED EMBODIMENTS AND DISCUSSION The preferred ranges ofconstituents in the fuel of this invention are from 40 to 55 percentisoparafiins, from 30 to 40 percent monocyclic naphthenes, from 15 topercent polycyclic naphthenes, and substantially no n-paraffins. Theisoparafiin content is especially critical since, if the fuel containsless than 40 percent isoparaffins, the luminometer number and the heatof combustion are adversely affected. If the isoparaflin content is.greater than about 55 percent, the fuel density is adversely affected.

The most preferred jet fuel composition consists of about 52 percentisoparaffins, about 30 percent monocyclic naphthenes and the balancepolycyclic naphthenes with substantially no n-paraffins.

Small quantities of n-parafiins can be tolerated in the fuels of thisinvention, but the n-parafiin content should never exceed about 6.5percent because of the detrimental effect of n-parafiin on the freezepoint. Preferably, the n-parafiins are substantially all removed fromthe jet fuel.

Briefly, the fuels of this invention are formed in four primary ways.First, they can be produced by totally hydrogenating a stove oil cutfrom selected straight run crudes and blending these hydrogenated stoveoil cuts with hydrogenated propylene tetramer or with hydrogenated alkytrimers. Propylene tetramer is substantially 100 percent isoparafiinsafter hydrogenation. The alky trimers, as noted, are a mixture of C to Chydrocarbons and are substantially 100 percent isoparafiins prior tohydrogenation so that the single stage hydrogenation does not have to besevere.

Second, the fuels can be produced by hydrogenating a stove oil out froma straight run stock to completion in two stages and removingn-parafiins, as by means of a molecular sieve or by extraction with aurea complex.

Thirdly, these fuels can be produced by hydrogenating the stove oil cutfrom a straight run stock to completion, extracting the normal paraffinsfrom the hydrogenated stock, as through the use of molecular sieves, andblending the resultant product with hydrogenated tertamer and/ or alkytrimers.

Fourth, the fuels can be made by hydrogenating to completion a stove oilfraction from a selected thermally cracked stock, removing n-parafiins,as through the use of molecular sieves, and blending with hydrogenatedalky trimers to form a low vapor pressure, high thermal stability fuel.

The purpose of the single stage hydrogenation of the alky trimers isprimarily to increase the thermal stability of these materials and thefuel into which they are blended. The hydrogenation is carried out at atemperature of from 250 to 850 F., a pressure of from 300 to 2,000p.s.i.g., a liquid hourly space velocity of from 0.2 to 6.0 and ahydrogen to oil ratio of from 1,500 to 8,500 s.c.f./bbl.

By blending alky trimers with a hydrogenated straight run stove oil orrefinery stream of high paraifinicity, the preferred proportions ofconstituents for high Mach aircraft jet engine fuel can easily beobtained. The trimers must be blended since they have a fuel densityless than that required for high Mach aircraft fuels and, due to theirweight, they have a very high viscosity at temperatures on the order of30 F. and lower. The aiky trimers when used as blending stock, due totheir high isoparaffinicity, may generally be used in quantities up to20 percent by volume of the fuel blend with a straight run hydrogenatedstove oil constituting the remainder. Greater than about 20 percent byvolume of the alky trimers detrimentally affects the viscosity of thefuel at low temperatures. The preferred range of additions of alkytrimers is from 10 to 15 percent by volume.

Propylene tetramer is available as a refinery stream product and hasalso been found, when hydrogenated, to make an excellent blendingcomponent for the jet fuel of this invention. The tetramer, as noted, isan olefin boiling in the range of 365 to 445 F. and is sulfur free sothat it can be hydrogenated in a single step. Hydrogenation of thetetramer can be accomplished under substantially the same range ofconditions as for hydrogenation of alky trimers.

Suitable blending agents for the tetramer have been found to be amixture of hydrogenated stove oils from naphthenic and intermediatecrudes such as a stove oil mixture containing from 25 to percentparaffins of which 99 percent are isoparaffins, from 38 to 48 percentmonocyclic naphthenes, from 22 to 28 percent dicyclic naphthenes and upto 2 percent tricyclic naphthenes. The use of hydrogenated propylenetetramer in the place of alky trimers is beneficial in some casesbecause the tetramer has an extremely low viscosity at low temperaturessince it is a lighter weight stock and has shorter carbon chains thanthe alky trimers. The major limitation on the tetramer as a blendingcomponent is its poor fuel density. Up to about 50 percent by volumetetramer can be used without adverse effects. The preferred range oftetramer addition, however, has been found to be from about 25 topercent by volume. Usually 25 percent by volume tetramer is required tobring the fuel isoparafiin level within the desired range. If greaterthan 45 percent by volume tetramer is used, however, the fuel densitydecreases to a value very close to the minimum 124,000 B.t.u./ gal.level.

The alky trimers and propylene tetramers are convenie'nt to use asblending stocks since they require only a single hydrogenation step andsince they both are obtainable as by-products of petroleum refineryprocesses.

A highly isoparafiin blending stock can also be obtained by theelimination of n-parafiins from an initially high 11- paraffin contenthydrogenated thermally cracked stock boiling in the stove oil range bytreatment with molecular sieves. For example, a hydrogenated thermallycracked stock boiling in the range of 292 to 672 F. having a highinitial paraffin content with a large percentage of nparafiins may betreated with a molecular sieve to remove the n-paraffins. A typicalthermally cracked stock of this nature is a refinery Combination UnitBubble Tower sidestream boiling in the range of 292 to 672 F. whichafter complete hydrogenation comprises about 12 to 20 percentn-parafiins, about 12 to 20 percent isoparaffins, about 44 to 52 percentmonocyclic naphthenes and about 15 to 23 percent polycyclic naphthenes.Although the nparafiin content of the stock is reduced by the sievetreatment, the isoparaffin content is not affected. A molecular sievehaving a pore size of 5 angstroms has been found to be most suited foruse in separation since it passes the n-parafiins but not theisoparafiins. The n-paraffins, alternatively, may be removed from thethermally cracked stocks by other methods such as by extraction with aurea complex to provide the isoparafiinic blending component desired.

It has been found that the thermally cracked stocks must be hydrogenatedin two stages. The first stage hydrogenation or hydrofinishing isnecessary to remove sulfur and nitrogen from the stock and may beconducted at a temperature from 250 to 850 F., a pressure from 300 to2,000 p.s.i.g., a liquid hourly space velocity of from 0.2 to 6.0, and ahydrogenation rate of from 1,500 to 8,000 s.c.f./bbl. The preferredfirst stage conditions are a temperature from 600 to 800 F., a pressurefrom 450 to 850 p.s.i.g., a liquid hourly space velocity from 0.5 to 2.0and a hydrogenation rate of 2,500 to 3,500 s.c.f./bbl.

The hydrogenation catalyst for the first stage must also be ahydrodenitrogenation and hydrodesulfurization catalyst. Therefore, itmust be a catalyst which is not fouled by sulfur and nitrogen such as asupported metal combination of a Group VIII metal and Group VIB metaloxides and sulfides. Typical catalysts of this variety arecobalt-molybdenum oxide, nickel-molybdenum oxide, cobalt-molybdenumsulfide, nickel-molybdenum sulfide, cobalt-tungsten sulfide,nickel-tungsten sulfide and molybdenum-tungsten sulfide on aconventional support material such as alumina or silica-alumina. Thefirst stage hydrogenation should be at least to 80 percent saturationand preferably to 90 or 95 percent saturation.

The second stage hydrogenation conditions are a temperature from 200 to850 F., a pressure of from 100 to 2,000 p.s.i.g., a liquid hourly spacevelocity of 1.5 to 6.0, and a hydrogenation rate of 1,500 to 6,000s.c.f./bbl. The preferred conditions are temperatures from 400 to 750F., pressures from 500 to 1,000 p.s.i.g., a liquid hourly space velocityfrom 0.5 to 4.0, a hydrogenation rate of 3,500 to 4,500 s.c.f./bbl.Hydrogenation in the second stage should be substantially to completionand at least 98 percent to form the component of the jet fuels of thisinvention. Platinum group metal catalysts and preferably platinum havebeen found to produce the best results in the second stage.

Low boiling cracked and partially cracked products of the initialhydrogenation step may be removed by a convenient separation processsuch as distillation of a 370 to 520 F. heart cut prior to second stagehydrogenation. Separation may also be accomplished by other means suchas hydrogen stripping or with molecular sieves. With some thermallycracked stocks, it may be possible to eliminate the initialhydrogenation step since the sulfur content is sufiiciently lowinitially and the necessity for the first stage hydrogenation isdependent on the sulfur content of the oil.

The final product of the hydrogenation and sieve treat ment comprises ahighly isoparafiinic blending component comparable to but not as heavyas the alky trimers discussed.

It has been found that a highly isoparaffinic blending material can alsobe provided by selecting a straight run stove oil which, afterhydrogenation, is relatively high in parafi'ins and has a high heat ofcombustion and fuel density and by removing substantially alln-parafiins from the oil. Stove oil from Four Corners crude has beenfound to be the only straight run stock which satisfies theserequirements. Typically, the stove oil fraction, boiling in the range offrom 290 to 520 F., of this crude when hydrogenated contains from 22 to30 percent isoparaffins, from 15 to 20 percent n-paraffins, from 35 to41 percent monocyclic naphthenes and from 15 to 20 percent polycyclicnaphthenes when hydrogenated in the twostage hydrogenation processalready discussed. The preferred conditions and catalysts for thetwo-stage hydrogenation have been found to be the same as thosediscussed for thermally cracked stocks.

The hydrogenated Four Corners stove oil typically has a heat ofcombustion of 18,771 B.t.u./lb., a fuel density of 124,658 B.t.u./gal.,a luminometer number of 84 and a freeze point of 40 F. After removal ofthe n-paraffins from the oil, the heat of combustion, fuel density andluminometer number remained substantially constant while the freezepoint decreased to below F. providing a full scope of excellentproperties for a jet fuel.

This invention may be further understood from a consideration of theforegoing discussion in conjunction with the following specific examplesof the high Mach jet fuel prepared in accordance with our invention. Theexamples are not intended to limit the scope of this invention beyondthat of the appended claims.

EXAMPLE 1 A fuel was prepared by blending 35 volume percent hydrogenatedalky trimers with 65 volume percent of a hydrogenated straight run stoveoil blend. The alkyl trimers used as a blending component in the fuelboiled in the range of from 372 to 522 F. and contained:

Percent by volume These alky trimers were hydrogenated in a single stepin the presence of a platinum group metal catalyst at 600 p.s.i.g., 500F., a liquid hourly space velocity of 1.0, and a hydrogen rate of 4,000s.c.f./bbl.

The stove oil blend comprised a mixture of 2 parts of a stove oil from anaphthenic type crude, i.e., a crude having from 55 to 65 percentnaphthenes, less than 20 percent paraffins and the balance aromatics and1 part of a stove oil from an intermediate type crude, i.e., a crudehaving from 45 to 55 percent naphthenes, about 30 percent parafiins andthe remainder aromatics. The stove oil blend was hydrogenated in twosteps the first of which was carried out at 750 p.s.i.g., 750 F., 1.0liquid hourly space velocity, and 3,000 s.c.f./bb]. in the presence of acobalt-molybdenum oxide catalyst on alumina. The second stage was at 600p.s.i.g., 500 F., 1.0 liquid hourly space velocity, and 4,000s.c.f./bbl. in

the presence of a platinum catalyst. The final fuel contained:

Percent by volume n-Parafiins 0.8 Isoparafiins 52.1 Monocyclicnaphthenes 29.5 Dicyclic naphthenes 17.2 Tricyclic naphthenes 0.4

This fuel was tested in the laboratory and found to have the followingproperties:

Gravity, API 43.8 Heat of combustion, B.t.u./lb. 18,770 Fuel density,B.t.u./gal. 126,025 Freeze point, F. Below 80 Viscosity, CS at 30 F.17.4

Luminometer number 74 7 Distillation, F.:

IBP 378 Rec. percent 97.0 Flash point, PMCC, F. 164

The fuel had good thermal stability at 700 F. The addition ofsubstantially 100 percent isoparafiinic alky rerun bottoms to the blendof stove oils, as shown, provided a fuel which was suitable as a highMach jet engine fuel. Although the paraifin content exceeded 50 percentthe freeze point of the fuel was still excellent.

EXAMPLE 2 A mixture of 10 percent hydrogenated alky trimers and 90percent of a hydrogenated Mid-east stove oil comprising 42.5 percent byvolume isoparafiins, 38.6 percent by volume monocyclic naphthenes and18.9 percent by volume dicyclic naphthenes was prepared. The alkytrimers were hydrogenated in a single step in the presence of a platinumcatalyst at a temperature of 500 F., a pressure of 600 p.s.i.g., aliquid hourly space velocity of 1.0 and a hydrogen to oil ratio of 4,000s.c.f./bbl. The stove oil was hydrogenated to completion in two stagesunder the following conditions:

First stage.Nickel-molybdenum oxide on alumina catalyst, 750 p.s.i.g.,750 F., 1.0 liquid hourly space velocity, and 3,000 s.c.f./bbl.

Second stage-Platinum catalyst, 600 p.s.i.g., 500 F.,

1.0 liquid hourly space velocity, and 4,000 s.c.f./bbl.

The fuel blend consisted of 48.3 percent by volume isoparafiins, 34.7percent by volume monocyclic naphthenes and 17 percent by volumedicyclic naphthenes.

This fuel was tested in the laboratory and found to possess thefollowing properties:

Gravity, API 43.5 Heat of combustion, B.t.u./lb. 18,750

Fuel density, B.t.u./ gal. 126,225

Freeze point, F. -80 Viscosity, CS at 30 F 16.7 Luminometer number 80Distillation, F.:

IBP 388 10% 403 50% 427 90% 479 EP 14 Flash point 164 EXAMPLE 3Propylene tetramer was hydrogenated to completion in one step under thefollowing conditions:

Platinum catalyst, 700 p.s.i.g., 500 F., 6.0 liquid hourly spacevelocity and 4,000 s.c.f./bbl.

The hydrogenated tetramer was blended with a hydrogenated naphthenic andan intermediate stove oil blend, as described in Example 1, to form afuel containing 45 percent by volume propylene tetramer and 55 percentby volume of the stove oil blend. This fuel has the followingcomposition:

Percent by volume n-Paraiiins 0.7 Isoparatfins 59.5 Monocyclicnaphthenes 24.9 Dicyclic naphthenes 14.5 Tricyclic naphthenes 0.4

Cal

8 When tested in the laboratory this fuel exhibited the followingproperties:

Gravity, API 46.0 Heat of combustion, B.t.u./lb 18,760 Fuel density,B.t.u./ gal. 124,543

Generally, the viscosity and luminometer number of the tetramer blendwere better than the alky trimer-stove oil blend but the fuel densitywas not as good.

EXAMPLE 4 Propylene tetramer, hydrogenated as in Example 3, was blendedwith a stove oil, hydrogenated as in Example 1, having the followingcomposition:

42.5 percent isoparaffins, 38.6 percent monocyclic naphthenes and 18.9percent dicyclic naphthenes.

The fuel blend formed was 20 percent by volume propylene tetramer andpercent by volume stove oil and had a composition consisting of:

Percent by volume n-Paraffins 7.7 lsoparatfins 50.7 Monocyclicnaphthenes 27.9 Dicyclic naphthenes 13.7

This fuel composition was tested in the laboratory and had the followingproperties:

Gravity, API 46.8 Heat of combustion, B.t.u./lb. 18,815 Fuel density,B.t.u./ gal. 124,310

Freeze point, F. 40 Viscosity, CS at -30 F 16 Luminometer number 78 Thefreeze point of this fuel was above that required for use in high Machjet engines and, thus, the fuel was treated with a Lindy 5A molecularsieve to remove nparafiins. The resultant fuel had the followingcomposition:

Percent by volume Isoparaflins 54.0 Monocyclic naphthenes 30.9 Dicyclicnaphthenes 15.1

This fuel blend was then tested in the laboratory and was found to havethe following properties:

Gravity, API 45.0 Heat of combustion, B.t.u./ lb 18,750 Fuel density,B.t.u./gal. 125,150 Freeze point, F. below 80 Viscosity, CS at 30 F.Less than 15 Luminometer number 80 Treatment of the fuel composition toremove n-paraffins thus produced a very beneficial eifect on the freezepoint and luminometer number of the fuel without serious detrimentaleffect on the heat of combustion.

EXAMPLE 5 A fuel was prepared by blending 7.5 percent by volumepropylene tetramer with 7.5 percent by volume alkyl trimers and percentby volume of a hydrogenated stove oil having the composition of thatused in Example 4. The

alky trimers and the tetramers were hydrogenated in a single step, as inExamples 1 and 3 respectively. The stove oil was hydrogenated in 2 stepsas in Example 1. The blended fuel was then passed through a Lindy 5Amolecular sieve to remove n-parafiins. The sieved fuel had the followingcomposition:

51.1 percent by volume isoparafiins, 32.8 percent by volume monocyclicnaphthenes, and 16.1 percent by volume dicyclic naphthenes.

This fuel was found to have the following properties:

Gravity, API 4.39 Heat of combustion, B.t.u./ lb 18,750 Fuel Density,B.t.u./ gal 125,945 Freeze point, F. Below 80 Viscosity at 30 F., CS15.3 Luminometer number 75.4 Flash point, PMCC, F. 162 Distillation:

IBP 387 Rec. percent 98.0

EXAMPLE 6 A stove oil out from a Four Corners crude was hydrogenated tocompletion under the two stage hydrogenation conditions of Example 1 andthen passed through a Lindy 5A molecular sieve to remove n-paraflins.The resultant stove oil was 30.3 percent by volume isoparaffins, 48.3percent by volume monocyclic naphthenes, and 21.4 percent by volumetricyclic naphthenes.

This Four Corners stove oil had the following properties afterhydrogenation and prior to removal of the n-paraffins.

Gravity, API 45.9 Heat of combustion, B.t.u./lb. 18,771 Fuel density,B.t.u./ gal. 124,658 Freeze point, F 42 Viscosity, CS at -30 F.Luminometer number 84 After removal of the n-paraflins, the fuel had thefollowiug properties:

After removal of the n-parafiins the fuel had an excellent viscosity andfreeze point. Four Comers Crude of the composition given has been foundto be the only crude which could be hydrogenated and sieved and thendirectly used as a fuel without blending.

EXAMPLE 7 A thermally cracked stock obtained from a refinery combinationunit bubble tower side stream boiling in the range of 292 to 672 F. washydrogenated under the two stage conditions set forth in Example 1 and a375 to 520 F. heart cut was distilled 01f to form a stock comprising byvolume 49.7 percent paraflins about 10 percent of which weren-parafiins, 32.8 percent monocyclic naphthenes, and 17.5 percentdicyclic naphthenes.

This thermally cracked stock was blended with alky trimers hydrogenatedas in Example 1 to produce a fuel comprising 85 percent by volume of thethermally cracked stock and percent by volume of the alky trimers.

This stock was tested in the laboratory and found to have the followingproperties:

Gravity, API 44.8 Heat of combustion, B.t.u./lb. 18,755 Fuel density,B.t.u./gal. 125,320 Freeze point, F. 60 Viscosity at 30 F., CS 13.51Luminometer number 83 Distillation, F.:

IBP 384 Although the stove oils of many crude oils were examined andnone was found which could be hydrogenated and used directly as a highMach aircraft jet fuel, it is theoretically possible that such a stoveoil might be available. Accordingly, with such a stove oil it would bepossible to produce high Mach aircraft jet fuels of the disclosedcomposition using only the two stage hydrogenation described.

Many modifications and variations of the invention, as hereinbefore setforth, may be made without departing from the spirit and scope thereofand therefore only such limitations should be applied as are indicatedin the appended claims.

We claim:

1. A process for forming a jet engine fuel for Mach 3 to 3.5 aircraftcomprising the steps of hydrogenating alky trimers at a temperature from250 to 850 F., a pressure from 300 to 2,000 p.s.i.g., a liquid hourlyspace velocity of from 0.2 to 6.0, and a hydrogen rate of from 1,500 to8,5000 s.c.f./bbl. in the presence of a platinum group metal catalyst tosubstantial completion to form a mixture of C to C isoparafiins;blending 7.5 to 20 percent by volume of said hydrogenated alky trimerswith a hydrogenated stove oil fraction to form a fuel having up to 6.5percent by volume n-paraffins, from 20 to 50 percent by volumemonocyclic naphthenes, from 10 to 25 percent polycyclic naphth-enes andthe balance isoparaffins.

2. A process as defined in claim 1 wherein the alky trimers are amixture of C to C isoparaffins consisting essentially of 8 to 15 percentby volume C 30 to 40 percent by volume C 10 to 25 percent by volume C 10to 25 percent by volume C 8 to 15 percent by volume C and 8 to 15percent by volume C isoparaffins.

3. A process as defined in claim 1 wherein said fuel is formed byblending about 7.5 percent by volume hydrogenated propylene tetramerwith 7.5 percent by volume of said hydrogenated alkyl trimer and aboutpercent by volume of a hydrogenated stove oil consisting essentially offrom 40 to 45 percent by volume isoparalfins 35 to 40 percent by volumemonocyclic naphthenes, and the balance polycyclic naphthenes.

4. A process as defined in claim 3 wherein said hydrogenated propylenetetramer consists essentially of up to 27 percent by volume Cisoparafiins, from 50 to 70 percent by volume C isoparaffins, from 3 to45 percent by volume C isoparaffins and up to 5 percent by volume Cisoparafiins and said hydrogenated alky trimers consist essentially of 8to 15 percent by volume C isoparafilns, 30 to 40 percent by volume Cisoparaflins, 10 to 25 percent by volume C isoparaflins, 10 to 25percent by volume C isoparafiins, 8 to 15 percent by volume Cisoparaffins and 8 to 15 percent by volume C isoparaffins.

5. A process for forming a high Mach jet engine aircraft fuelcomprising:

hydrogenating a refinery tetramer stream consisting essentially of byvolume up to 30 percent C olefins, from 50 to 70 percent C olefins, from3 to 45 perpercent C olefins and up to 5 percent C olefins, at atemperature of from 250 to 850 F., a pressure of from 300 to 2,000p.s.i.g., a liquid hourly space velocity of from 0.2 to 6.0 and ahydrogen rate of from 1,500 to 8,500 s.c.f./bbl. in the presence of aplatinum group metal catalyst;

providing a hydrogenated stove oil consisting essentially of from 30 to45 percent by volume isoparatfins, from 35 to 50 percent by volumemonocyclic napthenes, from 15 to 25 percent by volume polycyclicnaphthenes and substantially no n-parafiins;

blending a sufficient quantity of said tetramer with said stove oil toform a jet engine fuel having 20 to 50 percent by volume tetramer andthe balance stove oil, said fuel having a heat of combustion of at least18,750 B.t.u./lb., a fuel density of at least 124,000 B.t.u./gal., aluminometer number of at least 75, a freeze point of -75 F. or lower anda viscosity of less than 15 centistokes at 30 F.

6. A process as defined in claim 5 wherein said hydrogenated stove oilis prepared by hydrogenating at a temperature from 250 to 850 F., apressure from 300 to 2,000 p.s.i.g., a liquid hourly space velocity from0.5 to 6.0, and a hydrogen rate of from 1,500 to 8,000 s.c.f./bbl." inthe prescence of a hydrodesulfurizing catatyst;

separating a 370 to 520 F. heart cut from said hydrogenated product; and

hydrogenating said heart cut at a temperature of from 200 to 850 R, apressure of from 100 to 2,000 p.s.i.g., a liquid hourly space velocityof from 1.5 to 6.0, and a hydrogen rate of from 1,500 to 6,000s.c.f./bb1. in the presence of a platinum group metal catalyst.

7. A process for forming a jet engine fuel for Mach 3 to 3.5 aircraftcomprising the steps of:

hydrogenating a thermally cracked stock boiling in the range of 292 to672 F. to form a stock consisting essentially of from 12 to 20 percentby volume n parafiins, from 12 to 20 percent by volume isoparaflins,from 44 to 52 percent by volume monocyclic naphthenes, and from 15 to 23percent by volume polycyclic naphthenes;

conducting said hydrogenation in a first stage at a temperature from 250to 850 F., a pressure from 300 to 2,000 p.s.i.g., a liquid hourly spacevelocity of from 0.2 to 6.0, and a hydrogen rate of from 1,500 to 8,000s.c.f./-hbl. in the presence of a hydrodesulfurization catalyst and in asecond stage at a temperature from 200 to 850 F., a pressure from 100 to2,000 p.s.i.g., a liquid hourly space velocity of from 1.5 to 6.0, and ahydrogen rate of 1,500 to 6,000 s.c.f./ bbl. in the presence of aplatinum catalyst; and

blending said hydrogenated thermally cracked stock with a sufficientquantity of alkyl trimers to provide a fuel containing 85 percent byvolume thermally cracked stock and 15 percent by volume alky trimers andconsisting essentially of from 30 to 60 percent by volume isoparaffins,up to 6.5 percent n-paraffins, from to 50 percent by volume monocyclicnaphthenes and the remainder from 10 to percent by volume polycyclicnaphthenes.

8. A process, as defined in claim 7, wherein said thermally crackedstock consists essentially of about 49 percent paraflins, about 33percent monocyclic naphthenes and about 18 percent polycyclicnaphthenes, about 10 percent of said paraflins being n-paraffins.

9. A process, as defined in claim 7, wherein said alky trimers comprisea distribution of C to C isoparafiins consisting essentially of from 8to 15 percent by volume C from to percent by volume C from 10 to 25percent by volume C 2, from 10 to 25 percent by volume C13, from 8 to 15percent by volume C and from 8 to 15 percent by volume C 10. A processas defined in claim 7 further including the step of passing said fuelthrough a molecular sieve of sufficient pore size to extractsubstantially all n-paraffins from said fuel.

References Cited UNITED STATES PATENTS 3,125,503 3/1964 Kerr et a1.208-15 3,126,330 3/ 1964 Zimmerscheid et al. 208-15 3,155,740 11/1964Schneider 208-15 3,185,739 5/1965 Gray et a1. 208-15 3,175,970 3/1965Bercik et al. 208-212 3,231,489 1/1966 Mahar 208-15 3,242,066 3/ 1966Myers 208-15 3,369,998 3/1968 Berick et al. 208-210 3,367,860 2/1968Barnes et al. 208-15 FOREIGN PATENTS 836,104 6/ 1960 Great Britain.870,431 7/ 1961 Great Britain.

HERBERT LEVINE, Primary Examiner US. Cl. X.R.

